Cathode ray tube deflection system



April 2, 1940. H. o. ROOSENSTEIN ET AL 2,195,470

CATHODE RAY TUBE DEFLECTION SYSTEM Filed March 2, 1937 INVENTORS HANS O-ROOSENSTEIN GEORG P FFRATH BY ATTORNEY Patented Apr. 2, 1940 PA N omen,

Hans Otto Roosenstein and Georg Pafirath,

Berlin, Germany,

assignors to Tclefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 11.,v Berlin, Germany, a corporation of Germany Application March 2, 1937, Serial No. 128,565

In Germany March 3,1936

Y. is "Claims. c1. 250. 157 This-invention relates to cathode ray tubes;v

and in particular, to method and means of improving the deflection system forfsuch tubes-by the use ofpermanent magnetic fields. Accord 5" ingly, it is one of the objects of our invention to provide method and means "for rendering magnetic deflection systems of cathode ray tubes freer from distortions.

l In describing our invention, reference willbe Y made to the-drawing, in which: 7

Figs. 1 through'e show graphically scanning wave shapes for explaining our invention;

Fig. 5 shows schematically one embodiment of our inventionusing fixed magnets for eliminating dissymmetricaldeflectingfields;

Fig. 6 shows graphically the magnetic lines of force set up by the fixed magnet system shown in Fig. 5'; while.

Figs. 7 through 10 show schematically modifications of the embodiment of the fixed magnetic system shown in Fig. 5.

"If cathode ray tubes for television work are furnished with deflector coils disposed symmetrically in reference to the cathode ray, they require for their proper operation av saw-tooth shaped current in the said deflector coils, in other words,

in representing the shapeof the" current as a function ofv time, the area enveloped between the contour of the curve and the zero line above and below the neutral line must be of like size, In

other words, the current curve must be of a nature as shown in Fig. 1 or Fig. 2 'where the areas above the neutral line are hatched horizontally and those below it vertically. A symmetric shape of the current in this sense is necessary for the reason that in the customary form of the tube bulb presenting rotational symmetry, the fluorescent screen or the screen to be scanned by the cathode-ray pencil is positioned symmetrically to 40 the axis of the cathode ray pencil. Now, most circuit organizations designed toproduce a sawtooth shaped current curve operate in this manner that a dissymmetric rather than a symmetric form of sawtooth is generated. What is here u meant by a dissymmetric saw-tooth form is a form'such as illustrated in Figs. 3 and 4 which differs from the one illustrated in Figs. 1 and 2 by an additional D. C. component. This component need not necessarily be so large or marked that the entire sawtooth curve comes to lie on one'side of the neutral line: indeed,what is to be regarded as dissymmetric according to the invention is also a current curve in which the area located upon one side of the neutral line is either greater or smaller than the area upon the respec-' in the deflection-flux is either lessened or elimtive opposite side thereof. In order to eliminate this D. 0; component, that is to say, in order to insure sawtooth shapedcurves as shown, for example, in Figs. 1 and 2 from waves shown in Figs-3 and 4, the use of a'push-pull amplifier 5 stage has'been suggested. The invention-is concerned with simpler meansadapted to symmetricize a dissymmetric sawtoothcurve, and the same consists in disposing concentrically to the tube axisa'steel ring, pref- 10 erably anop'en winding consisting of tape or wire,- the said winding being permanently ma netized in such a way thatthe D. C.-c'omponent included inated. 15

An exemplified embodiment of the invention which is here applied to a receiver Braun tube is illustrated in "Figs. 5 and 6 of the accompanying drawing.

Referring to the drawing, 10 denotes a glass 20' I bulb which consists-of a cylindrical and a truncated-cone shaped part. Upon the bottom end of thetube'is applied the fluorescent substance ll. Inside the glass bulb is mounted a heated cathode l2; moreover, a control means or Wehg5 nelt cylinder (shield) l3, and aso-called first and second anode (gun) l4 and I5, respectively, whereby is insured at the same time the focus- Y ing of the pencil. Outside the tube is a deflector coil .l6, for the horizontal deflection, whereas .30

' vertical deflection is accomplished by the agency of a pair of coils which is traversed by a current of sawtooth shape obtained from a push-pull circuit organization. Exteriorly of the tube isaccommodated an open winding I! which is posi- 35 tioned, symmetrically in reference to the tube axis. The said winding is subject to "permanent magnetization or energization in such a way that the north poles and the south poles are distributed thereon as illustrated in Fig. 6. This dis- 40 tribution insures a field which will be adequately homogeneous inside thecross-section of the tube, with the result that the deflecting effect of the D. C. component of the dissymmetric sawtooth current is either diminished or entirely elimi- 45 nated. Fig. 6 roughly shows in a schematic manner the shape of the permanent field.

Fig. 7 shows another embodiment, Le, a steel .ring consisting of an open Winding made up of square steel wire. In its stead also a steel hand or 60 tape or ribbon could be employed of the kind shown in Fig. 8., Under certain circumstances recourse could also be had to a steel ribbon as shown'in Fig. 9, or else a solid (massive) form of 3 construction as indicated in Fig. 10. In the form shown in Fig. 9 or Fig. 10 it must be kept in mind that there is a likelihood of .certain eddy-currents being set up as a result of the saw tooth component of the deflection field. Whether in any given practical instance an embodiment as in Fig. 9 or in Fig. 10is feasible will depend upon the frequency and the amplitude of the sawtooth current and also upon the construction and the position of the deflector coil in question. When an iron-closed coil is used, or if the distance between the deflector coil and the steel. ring is suflicient, the risk of eddy currents being set up will be slight.

An arrangement according to this invention is' adapted not only, as assumedin the exemplified embodiments described by reference to Figs; 5

and 6, to the elimination of the effect of the D. C'. component in the sawtooth current, but. will also be found useful either alone or in combination with other means, to obviate theinfluence of the terrestrial-field or the influence of stray interference fields presenting time constancy.

j Anarrangement as here disclosed could also be used for the purpose to eliminate the influence of the D. C. component-of two pairs of coils designed to insure horizontal and vertical deflection. For this purpose, all thatis necessary is'to magnetize the steel ring according to Figs. 6 to 10 to a sufficient extent and to so adjustthe same that the direction of the permanent field set up thereby will be opposite and contrary to the geometric sum total of the D. 'C..componentsof the two deflector fields.

Having described our invention, what we claim 1. In combination, a cathode ray tube having a cylindrical neck l portion, an electron gun mounted within the neck portion, magnetic deflecting coils positioned symmetrically about the cylindrical neck portion, and a plurality of fixed circular magnets closely adjacent each other and longitudinally'displaced, from the deflecting coils and'concentric with the circular neck'of the tube said magnets producingamagnetic field perpendicular to the axis of the cylindrical neck portion. g

2. In combination, a cathode ray tube having a cylindrical. neck portion, an electron gun mounted within the neck portion, magnetic deflecting coils positioned symmetrically about the cylindrical neck portion, and a magnetized severed iron .coil closely adjacent each other and longitudinally displaced from the deflecting coils and concentric with the circular'n'eck of the tube said magnets producing a magnetic fleld perpendicular to the axis of the cylindrical neck portion. v i

3. In combination, a cathode ray tube having a cylindrical neck portion, an electron gun mounted Within the neck portion, ma gnetic' deflecting 25 

